added client management panel

- added classes for displaying the client management panel
- added class for displaying the client info
- added page to display a list of clients
- added page to display OpenVpn client information
- added diagram with OpenVpn certificate revocation process

client/ui/models/clientManagementModel.h

@@ -0,0 +1,42 @@
+#ifndef CLIENTMANAGEMENTMODEL_H
+#define CLIENTMANAGEMENTMODEL_H
+
+#include <QAbstractListModel>
+
+#include "settings.h"
+
+class ClientManagementModel : public QAbstractListModel
+{
+    Q_OBJECT
+
+public:
+    enum ClientRoles {
+        NameRole = Qt::UserRole + 1,
+        CertIdRole,
+        CertDataRole
+    };
+
+    struct ClientInfo
+    {
+        QString name;
+        QString certId;
+        QString certData;
+    };
+
+    ClientManagementModel(std::shared_ptr<Settings> settings, QObject *parent = nullptr);
+
+    void clearData();
+    void setContent(const QVector<ClientInfo> &data);
+    int rowCount(const QModelIndex &parent = QModelIndex()) const override;
+    QVariant data(const QModelIndex &index, int role = Qt::DisplayRole) const override;
+    void setData(const QModelIndex &index, QVariant data, int role = Qt::DisplayRole);
+
+protected:
+    QHash<int, QByteArray> roleNames() const override;
+
+private:
+    std::shared_ptr<Settings> m_settings; //TODO remove this?
+    QVector<ClientInfo> m_content;
+};
+
+#endif // CLIENTMANAGEMENTMODEL_H